The Rijidij light pole I fitted to my D3 had a 2 way switch on it. In position 1 I have connected to traxide cabling at rear, (downstream of engel power socket fuse) and the other I spilced into the reverse circuit. Earth connected to earth stud.
I also fitted an over ride switch in the interior to ensure kids dont accidently change positions 2 to 1 and flatten my aux battery.
Bloody great bit of kit!! Murray builds a ripper D3/D4 RWC too.

